Fluid coupled fiber optic sensor

ABSTRACT

A passive transducer apparatus and method of use for producing a useful output light signal in response to a sensed condition. The sensed condition varies the light emitted from a first fiber optic light conductor that is apparently captured or detected by a second fiber optic light conductor. The light captured by the second or collector fiber optic member is the useful output signal which may be made proportional to the sensed condition. The apparent change in light capture may be caused by a relative change in geometry of the fiber optic members, by variation in the coupling fluid or by an external optical member.

This application is a divisional of application Ser. No. 025,711, filedMar. 13, 1987, now U.S. Pat. No. 4,839,515.

FIELD OF THE INVENTION

The present invention relates to the field of transducers and moreparticularly to a transducer using light energy.

CROSS-REFERENCE TO A DISCLOSURE DOCUMENT

The subject matter of the present application is partially contained indisclosure document No. 155,915 filed Sept. 15, 1986 with the UnitedStates Patent and Trademark Office.

BACKGROUND OF THE INVENTION

Light is a form of electro mechanical radiant energy that is detectedvisually or by appropriate sensors. Light is considered to have a cyclicwave energy pattern and ordinarily move or project in a straight linecalled a ray. When light energy as an incident ray strikes an objectsome is reflected, some is absorbed and some is transmitted.Conventionally light travels in a straight line and may be reflected orsubject to refraction in the same manner.

Refraction is the recognized scientific principal which causes a bendingor change in the direction of the ray or propagation of light as itpasses or is transmitted from one light transparent material or mediumto another. Such refraction bending is considered completely reversiblein as the identical bending occurs in either direction. Both the anglesof incidence and refraction (or reflection) are conventionallydetermined by reference to the normal which is located at right anglesto the plane of the interface of the two mediums or materials. Inreflection, the angle of light ray incidence is equal to the angle ofreflection.

The angular path of the refracted ray is determined by the index ofrefraction of the material receiving the incidence light ray. Theabsolute index of refraction of any medium is defined as the index ofrefraction of the medium relative to vacuum. The absolute index ofrefraction is usually called just the index of refraction on therefractive index of the medium. The greater the index of refraction thegreater the optical density and the greater the angle of bending.

Total reflection is another light energy phenomenon that occurs at theinterface of two mediums of different optical density (an opticallydenser material inherently also has a higher index of refraction). Alight incident ray within the denser medium having an incidence angle togive an angle of refraction greater than 90° is totally internallyreflected and no light passes into the other medium. The angle ofincidence for which the angle of refraction is 90° or normal is calledthe critical angle. Light at angles of incidence at or greater than thecritical angle is totally internally reflected within the denser medium.Total internal reflection can only occur only for light within a mediumof higher optical density at an interface surface with a medium of lowerdensity. Although the principle is based on the second law ofrefraction, the effect is called total internal reflection.

Fiber optics employ the total internal reflection to achievetransmission of light with greater effectiveness and relatively smalllight loss or attenuation. Fiber optics serve as dielectric opticalwaveguides or conductors for directing the propagation of light in aselected path. Because fiber optics are basically passive devices (nomoving parts) they are durable and simple in operation and thereforhighly desirable from a reliability and maintenance standpoint.

Fiber optic sensors using the principle of internal refraction areknown. For examples see U.S. Pat. Nos. 3,282,149, 4,286,468 and4,564,292. All of these determine the amount of light transmittedthrough a single optic waveguide fiber as a function of the light lossoccurring at a selected sensor portion.

U.S. Pat. No. 3,282,149 to Shaw et al. is entitled "Linear PhotoelectricRefractometer". The Shaw patent sets forth the then state of the art insome detail including certain mathematical light relationships. Inaddition, by measuring the transmitted light through a straighttransparent rod where the index of refraction of the surroundingmaterial is less than that of the rod, some of the light reflected atangles less than the critical incidence angle and all of the lightreflected at angles greater the critical angle will be retained (totalreflection) in the rod. By measuring the transmitted light in the rod,the index of refraction of the surrounding material can bemathematically determined. The actual source of light is not criticaland good results are obtained from an ordinary heating tungstenillumination element light bulb.

A conventional photodetector system is used to measure the value of thelight retained in the rod and generate a suitable responsive electricalsignal. Using known apparatus, this electrical signal is processed in apredetermined manner and the desired information is then usefullydisplayed. The disclosed device of the Shaw patent is used for measuringthe index of refraction of a fluid using a helically coil shapedtransparent sensing body having at least 360° of curvature and made of atransparent dielectric (electrically insulating) material having anindex of refraction higher than that of the substance to be measured.The sensing element shape enables the determination of the index ofrefraction without the necessity to determine the angle of incidenceoptically. Such arrangement is particularly desirable if a photoelectricsensor or detector is used to measure the light intensity for making thedetermination. Because the light intensity in the rod is measured, thepresence of color, bubbles or solids in the fluid being measured forrefraction does not adversely affect the information generated.

U.S. Pat. No. 4,564,292 to Omet also discloses a portable photoelectricrefractometer for measuring the index of refraction of a sample medium.The disclosed device measures the transmission of light through aU-shaped or curved unshielded fiber optic sensor mounted on a probe. Asthe light transmission is a substantially linear function of the indexof refraction greater accuracy and reliability can be obtained in use ifthe temperature factor can be controlled. To eliminate the potentialsource of temperature error, a reference U-shaped fiber optic sensor isplaced in the probe in contact with a reference fluid along with asimilar shaped fiber optic sensor for contacting the fluid beingexamined. By a suitable delay in making a reading until a commontemperature is reached, the potential for measurement error from atemperature difference of the fluids are eliminated.

In U.S. Pat. No. 4,286,468 to Altmen a method and apparatus for sensingor transducing sound wave motion by determination of total lighttransmitted by an optical fiber is disclosed. This patent, which isentitled "Frustrated Total Internal Reflection Fiber-Optic Small MotionSensor For Hydrophone Use", discloses a hydrophone transducer fordetecting acoustic pressure wave signals in the ocean. The hydrophonetransducer operates by sensing a change in the refractive index of thefiber as the acoustical pressure changes. Such changes in refractiveindex effect a phase delay of the transmitted light which is thenmeasured and compared with a reference to detect the sound waves.

The unclad spiral portion of the Altmet Patent fiber optic sensor ispositioned adjacent to a flat plate and the space therebetween filledwith a fluid having a low optical loss characteristic and a refractiveindex lower than the fiber core. Because of the lower refractive index,the transmission of light through the unclad coiled fiber optic sensoris dependent on total internal reflection at the core interface. Alsopresent adjacent the unclad sensor portion is an evanescent light wavefield which externally surrounds the sensor. The evanescent light fieldis made available or created by removing the optical cladding. To theextent that this surrounding light field is intercepted by a material ofhigher refractive index than the fluid, the total internal reflection isdiminished and the apparent light transmission loss of the optic sensorincreased. The closer the movable field light interceptor plate moves tothe fiber optic sensor the greater the apparent loss of light. Becausethe plate frustrates the otherwise total internal reflection of thefiber optic sensor, this type of modulation phenomenon is sometimescalled "frustrated total internal reflection". The resulting change inthe phase, not intensity, of the fiber optic transmitted light can bemeasured and displayed using conventional techniques.

Another group of fiber optic devices uses a liquid core having a quartzcladding. By modifying the refractive index of the liquid core to varythe amount of light entering into or escaping from the core a usefulfeature is obtained. Examples of such devices are disclosed in U.S. Pat.Nos. 3,819,250 and 4,201,446.

Kibler U.S. Pat. No. 3,819,250 is entitled "Temperature SensitiveFiber-Optic Devices" and discloses three embodiments of a low light lossfiber optic coupler invention. The embodiment of FIG. 1 is a wideaperture coupler while the embodiment of FIG. 3 is a directional lightcoupler. FIG. 2 is a small radius bend guide coupler used to reducelight loss. All three embodiments utilize a temperature control toenhance effectiveness of the device. The reversible wide opening oraperture coupling enables the quartz cladding to introduce light intothe liquid core at a large critical angle in the heated region. Thelight accepting property of an optical fiber is normally called thenumerical aperture and often limits the amount of transmitted lightcaptured. The numerical aperture, a mathematical measure of thelight-accepting property of the sensing fiber optic core is controlledby the temperature of the coupling fluid. In the embodiment of FIG. 1the disclosed fiber optic sensors employ a quartz cladding or coatingand a dielectric liquids to enhance the light accepting or radiatingcoupling.

the normal light loss in the bend coupler (FIG. 2) is reduced by coolingthe core and cladding to increase the difference in refractive index andincrease the total internal reflection.

The directional coupled embodiment (FIG. 3) employs two parallel quartzfiber optic rods embedded in a dielectric coupler liquid (carbontetrachloride). While structurally similar to the present invention, thedisclosed function, operation and purpose are entirely different.Controlled temperature variations of the disclosed coupler structurewill transmit or couple different amounts of refracted light between thetwo rods due to the relative change in the indices of refraction of theliquid and the quartz rods. With this arrangement the amount of lightcoupled from one rod to the other is determined by the externaltemperature controller.

U.S. Pat. No. 4,201,446 to Geddes et al. discloses a fiber optic sensordevice for determining an unknown temperature. The disclosed sensor is aliquid-core optical fiber contained in a transparent glass capillarytube that is mounted in a conventional single fiber optic conductor at adesired remote sensing location. The liquid core of the sensor portionhas a temperature dependent index of refraction over a given temperaturerange. The numerical light aperture of the disclosed photoelectricelectric sensor varies continuously from zero to the maximum valuesensed by the fiber optic sensor. In another embodiment a conventionalunclad fiber optic core is immersed in a liquid having a temperaturesensitive refractive index.

Fiber optic core interconnection is known and essential for commercialoperation whether classified as a connector, a splice or a coupler.Splices are usually considered to be fusion or other permanentend-to-end joints between the cores of two separate fibers. Connectorsare usually considered to be demountable interconnections while couplersare usually considered optical connectors that redistribute particularlylight energy between two or more fibers. Collectively all of thesedevices seek to connect separate fiber optic fibers with a minimum ofattenuation or loss of light.

Also, fiber optic couplers have been devised using a liquid medium tocouple light from one fiber to another either from butt end to butt endor from unclad core to unclad core via the cylindrical surfaces. See,for example previously mentioned U.S. Pat. No. 3,819,250 (FIG. 3 anddescription at col. 4 lines 40-56) regarding an external temperaturecontrolled directional light coupler. As noted previously the couplingrelies on external temperature control of the fluid to a change therefractive index to permit light transmission.

The basic transduction mechanism employed in many known fiber opticsensors is the phase modulation of coherent light guided through asection of single mode fiber by the action of a detected energy field.Chapter 4 of the publication entitled "Fiber Optic Sensor TECHNOLOGYHANDBOOK" published by Dynamics Systems, Inc. describes the known formsor configurations currently employed in fiber optic sensors. A commonaspect of the mentioned transducers or sensors is the splitting andrecombing of the light beams to determine a light phase shift formeasuring the condition with such transducers.

SUMMARY OF THE INVENTION

The present invention relates to the field of a transducer using a lightenergy signal output and employing a pair of fiber optic light waveguideconductors operably coupled by a selected coupling fluid. Underoperating conditions a reference or base intensity conical pattern oflight is transferred through the coupling fluid from the emitting fiberoptic conductor to the receptor fiber optic conductor. The sensedphysical condition of the transducer varies the light intensitytransferred to or apparently detected by the receptor fiber opticconductor from the emitter fiber optic conductor. The condition sensedmay vary the transmitted light by effecting an actual or operatingchange in relative position of either or both fiber optic waveguides orof the coupling fluid or fluids. Actual or relative movement of externalmembers may also be used to vary the transmitted light received by thereceptor or light collecting wave guide. The physical condition sensedmay be used to modify the coupled light path in any desired manner toproduce an apparent change in light intensity. This apparent change inlight intensity of the detector fiber optic member is the transduceroutput signal that may be measured by known light detector apparatus andthe change in transducer sensed condition determined by conventionalprocessing in suitable electrical or electronic means of the receivedmeasured signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, in section, of a first embodiment of thetransducer apparatus of the present invention having a pair of spacedfiber optic light conductors showing a coupling light path between theconductors;

FIG. 2 is a view taken along line 2--2 of FIG. 1;

FIG. 3 is a view similar to FIG. 1 showing another manner ofmodification of the light path between the fiber optic conductors;

FIG. 4 is a view similar to FIG. 1 with the fiber optic light conductorsangularly disposed and showing the light path between conductors;

FIG. 5 is a view, similar to FIG. 1, of a modified form of the presentinvention having an external light path control member;

FIG. 6 is a view taken along line 6--6 of FIG. 5.

FIG. 7 is a view similar to FIG. 6 showing different light paths betweenthe fiber optic light conductors.

FIG. 8 is a view similar to FIG. 5 of another form of the external lightpath control member;

FIG. 9 is a side view, in section, of another form or embodiment of thepresent invention;

FIG. 10 is a view similar to FIG. 9 of still another form or embodimentof the present invention;

FIG. 11 is a side view, in section, of another embodiment of the presentinvention;

FIG. 12 is a view taken along lines 12--12 of FIG. 11;

FIG. 13 is a schematic view of a sensor system using the apparatus A ofthe present invention;

FIG. 14 is a view taken along the longitudinal axis of a fiber opticconductor showing the emitted light pattern;

FIG. 15 is a side view in section of another embodiment of the presentinvention; and

FIG. 16 is a view taken along line 16--16 of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 illustrates a preferred embodiment of the transducer orcondition sensor apparatus of the present invention, generallydesignated A. As used herein the term transducer is to be considered inits broadest sense of detecting a condition or of the conversion of anyphysical variable into a useful output signal. By way of example, butnot in limitation, the conditions sensed by the apparatus A includetemperature, pressure, index of refraction, movement (strain) and soforth. Those skilled in the art ill immediately appreciate the unlimitedpossibilities for packaging the present invention as a sensor ortransducer A for monitoring any condition.

As illustrated in FIG. 1, the sensor or transducer apparatus A includesa first, source or emitter fiber optic member or light waveguide 20 anda second, target or receptor fiber optic member or waveguide 22optically coupled by a suitable fluid generally designated F. The fiberoptic members 20 and 22 are employed or utilized as conventional opticalwaveguides for highly efficient transmission of light into and throughthe sensor apparatus A. The exact structural support arrangement of themembers 20 and 22 and containment chamber (not illustrated) for thefluid F ar well within the level of skill in the art and may be left toeach specific application. The transducer apparatus A produces a usefuloutput signal with the light apparently captured by the target fiberoptic member 22 with the sensed physical variable controlling theintensity of the light apparently captured. Either or both of the fiberoptic members 20 and 22 may be coupled directly with other fiber opticmembers to form a conventional desired light guide path to and from theapparatus A.

As illustrated in FIG. 13, the sensor apparatus A is preferably employedin a physical condition detector system, generally designated S. Thesystem includes a conventional fiber optic light source 24 that isoptically coupled to the fiber optic conductor 26 which is operablyinterconnected with fiber optic light emitter member 20. With thisarrangement the light output of the source 24 is present in the emittermember 20. A suitable light sensor 28 is optically coupled with fiberoptic conductor 30 that is interconnected with receptor fiber opticmember 22 of the apparatus A. The light captured by the receptor member22 is thus present or detectable by the sensor 28. This arrangement alsoenables the sensor apparatus A to be located remotely relative to theother components of the detector systems which are preferably located ina protective environment.

The detector system S includes a suitable conventional electrical orelectronic processor 32 which receives signals from both the source 24and sensor 28. With these two input signals the previously calibratedprocessor 32 automatically determines the condition sensed by theapparatus A and displays or records such information on suitableconnected known display apparatus 34. The output signal of the processor22 is transmitted to the display apparatus through conductor 36 andwhich may also be connected to a controller (not illustrated) of thecondition sensed by the apparatus A to form a conventional automaticfeedback controller or servo arrangement (not illustrated). The feedbackcontroller automatically adjusts the operation to maintain the conditionsensed by the apparatus A at a desired level or range.

The fiber optic members 20 and 22 may be selected from many of the nowcommercially available conductors having a wide range of properties,operating conditions and the like as well known to those skilled in theart. The actual operating conditions of the apparatus A will in alllikelihood determine the actual selection of the most suitable fiberoptic members. In general, such fiber optic members 20 and 22 have acentral cylindrical conductor core 20a or 22a having a relatively thincladding or external coating 20b or 22b formed or deposited thereon, asillustrated in FIG. 1. While the present invention will be described asa cylindrical core waveguide for member 20 and 22, it will be understoodthat those skilled in the art may employ waveguides of other thancircular cross section. For example, optical fiber ribbons or ofrectangular cross section may be selected. The cladding 20b and 22bnormally serve to protect the cores and prevent attenuation or loss ofthe transmitted light signal from the conductor core 20a and 22b. Thecladding 20b and 22 b is normally an optically transparent material,with a reflective index lower than the core 20a or 22b, placedexteriorly or outside the core material of an optical waveguide thatserves to reflect or refract lightwaves in order to confine the light tothe core.

In order to form the coupling light path between the members 20 and 22the exterior surface cladding of each is stripped or removed for apredetermined distance of, perhaps, one centimeter, and each core end20c and 22c is cleaved. The term cleaving is used in its conventionalsense in this art as meaning the shaping of the core end to an opticallyflat surface. Even with the cleaved ends 20c and 22c, light will escapeor radiate from the unclad portions or windows 20d and 22d formed on themembers 20 and 22, respectively. The cleaved ends 20c and 22c may thenbe coated, as desired, with either a highly reflecting substance ornon-reflecting, substance or opaque end caps 40 and 42 to insure nolight or light beam will escape or enter from the cleaved ends 20c and22c.

The other end (not illustrated) of the fiber optic member 20 is thencoupled either indirectly by conductor 26 or directly to a light source24 and the first end 20c dipped into a suitable calibration vessel V(FIG. 14) having a quantity of clear light coupling liquid of knownrefractive index higher than that of the core 20c to avoid totalinternal reflection. The end 20c is then immersed for a desired distanceor depth of, perhaps, one half centimeter in the liquid L. If desiredthe entire window 20d may be immersed in the liquid L. A whitecalibration card C is also disposed in the liquid L a certain distanceor depth below the end 20c and at right angles to the longitudinal axisof the fiber optic core 20a. It will then be seen from FIG. 14 that acone shaped light pattern has escaped from the fiber core peripheryforming a concentric circular light ring pattern 34 on the white card C.That the radiated light from the window 20d is a hollow cone of light 34can be shown by changing the depth of the white card C without changingthe amount of depth of fiber immersion. The angle of the cone shapelight pattern 34 is determined by the refractive index of the liquid Lwhich may or not be the same as that of the coupling fluid F. Ifconductor cores of other shapes are employed or the window 20d is formeddifferently, the pattern 34 will have a different shape. But any certainpattern may be used in the present invention. The light ring 34 displayverifies both the absence of voids or holes in the light pattern 34transmitted through window 10d and the angular relationship.

The calibration and verification of the receptor fiber optic member 22can be accomplished in the identical manner because of the reversibledirection path property of light. By reversing the system S connectionsthe emitter and receptor members 20 and 22 may, if some embodiments ofthe apparatus A, be interchanged in use.

After verification of the proper angular and homogeneous density of thelight path through windows 20d and 22d the fiber optic member 20 and 22,are assembled in the apparatus A in the various positional relationshipillustrated in order that the liquid emitted from window 20d is directedby the coupling fluid F to strike the window 22c to enable at least someof the light to be captured in the core 22a.

In FIG. 1, and the other Figures, the communicating light coupling pathbetween and internally of members 20 and 22 and coupling fluid F isillustrated by unreferenced light ray arrows. FIG. 2 illustrates theradial intersection of the light field rays produced by emitterconductor member 20 by receptor conductor member 22. The dotted lightrays within receptor member 22 indicates the internal refractive guidepath of the light captured through window 22d by controlled placement orrelative position of the members 20 and 22. The dotted line light raysinternally of member 20 illustrated the portion of the light path priorto radiation through window 20d. It will be understood that variousintermediate reflective and refractive surfaces (not illustrated) may beused to control the light paths without departing from the scope oroperation of the present invention.

The angle of this illustrated light cone depends on the difference ofrefractive index between the fiber cores 20a and 22a and the liquid L,on the Numerical Aperture of the fiber core 20a, assuming multimode, andfinally, on the beam spread of the light generated by source 24. For aparticular case, this angle may range up to 25 degrees. By the principleof reversibility of light propagation the adjacent collector fiber opticmember 22 may receive or collect and then transmit this same light tothe optical detector 28 for measurement.

By varying the geometrical light path relationship between the fiberoptic source member 20 and receiver member 22 we can obtain an intensityvariation of the transmitted light between fibers 20 and 22. Suchvariation in geometry or relative position can be accomplished by anynumber of suitable means. For example, an external physical variable canbe used to alter the geometrical light transfer relationship and in sodoing constitute a transducer of that physical variable into aproportional output signal.

In FIG. 1, three light ray paths are illustrated from the window 20d ofthe emitter member 20 to the collector member 22. The middle rayrepresents the approximate center of the light path in the illustratedplane while the two outer rays represent the approximate outer edges ofthe conical ring like lighted zone emitted by member 20. In the plane ofFIG. 2 the angled radial projection of the light rays from member 20 tothe receptor member 22 is illustrated while FIG. 14 illustrates thelight pattern 34 from the window 20d. Relative movement of the member22, while maintaining the parallel relationship with member 20, radiallytoward the member 20 as indicated by an arrow adjacent end cap 42 willincrease the number of light rays or light intensity captured by thecollector window 22d of the receptor member 22. Likewise, the relativespacing movement of the parallel disposed collector member 22 away fromthe emitter member 20 will reduce the intensity of the light signalcaptured by the collector window 22d. By the apparatus A securing themember 20 to a fixed support and the member 22 to a variable positionsupport, the relative position of the members 20 and 22 can bedetermined as well as the change in position by the light intensitysensed by calibrated detector 28. An example by way of description andnot limitation of the use of the embodiment of FIG. 1 would be intransducing the relative distance, positioning or spacing betweenoperating machine parts. In this application, the apparatus A needs onlyto be arranged such that the monitored condition effect some parallelspacing reciprocation of the collector member 22 to produce aproportional output signal.

The arrow adjacent the end cap 42 of the collector 22 in FIG. 3illustrates longitudinal reciprocation movement, in either direction, ofthe receptor member 22 for also varying the window 22d effectivelyexposed to the light emitted from member 20. In this embodiment theparallel spacing is constant, but longitudinal movement of the collector22 varies the light collectible by window 22d. An example of the use ofthe embodiment in FIG. 3 again by way of description and not limitationwold be reciprocating movement of a valve stem (not illustrated) of aremote valve. Such stem could also be mounted on a fluid pressuresensing diaphragm for determining fluid pressure conditions. Whilemovement of the parallel disposed collector member 22 has beenillustrated and described, it will be understood that any relativemovement or change in positional or geometric relationship of 20 and 22is all that is required to effect a change in the light detected bywindow 22d of collector 22. Such effect, function or result can also beachieved by actual physical movement of either the emitter 20 or thecollector 22.

Such effect can also be achieved by a change in a relative angular orgeometric relationship of the member 20 and 22 as illustrated in FIG. 4.In this figure, the arrows indicate relative rotary or swinging motionbetween the members 20 and 22. A slight change in the angle of incidentlight rays on the collector window 22d, under certain conditions, canhave a major proportional change in the captured light intensity. Thetransducer could thus serve as a rotational movement sensor ormisalignment detector. Such angular movement could be created bypressure, temperature, gravity or other physical condition by suitablearrangement.

It will be appreciated that any relative physical movement between themember 20 and 22 that will vary the geometric relationship therebetweenwill also vary the light apparently or actually transmitted intoreceptor member 22 which can be detected as a proportional light signalindicator of such movement. Because of the extremely short wave lengthsof light energy, an extremely sensitive transducer A for converting suchmovement into light energy is provided.

Equally significant is the ability to sense an apparent relativemovement or change in transmitted light caused by the coupling fluid orfluids. In the embodiments of FIGS. 1-3, a single, contained, commoncoupling fluid F having a known uniform index of refraction isdescribed. Other known light directional control means, such asreflecting mirrors, refracting prisms or shutters may be positioned inthe coupling light path provided by the fluid F. In such cases, theliquid refractive index is maintained constant and the entire light pathgeometry is immersed in the coupling fluid. The suggested modificationof the light path by such directional control means employs recognizedtechniques known to those skilled in the art and need not be set forthin detail.

In a second disclosed type of arrangement of the apparatus A, theemitter and receptor members 20 and 22 we assume a constant physicalgeometry (passive operation) and are coupled by a fluid of knownrefractive index but the coupling fluid interface with another or secondfluid of a second refractive index is moved along the unclad fiberwindows 20a and 22d. The second fluid provides a different coupled lightpath so the transmitted and captured light is proportional to or afunction of the interface location. In essence, the second fluid servesas an shield or shutter.

In FIG. 9, a preferred embodiment having a physical geometryrelationship of the members 20 and 22 similar to that of FIG. 1 isdisclosed. The emitter fiber optic wave guide member 20 is fixed inposition relative to the receptor member 22 by the apparatus A in anyconventional manner. In this embodiment, two coupling fluids F₁ and F₂are employed. The fluid F₁ is preferably a liquid to insure separationfrom fluid and formation of a distinct fluid interface Q with the secondF₂ which is preferably a vapor phase or gas having a differentrefractive index from that of liquid F₁. However, any two fluids whichwill constantly maintain an interface or level without intermixing maybe employed. The fluid F₂ is preferably not an optical coupler of themembers 20 and 22 and therefor serves as a shutter or shielding for thereceptor member window 22d. If the fluid F₂ is a coupler, the window 22dshould be positioned so that the index of refraction prevents lighttransmission or communication. Air is not a good coupling fluid whichmakes the embodiment of FIG. 9 attractive for use as a liquid levelsensor open to the atmosphere liquid storage tanks. With the opticalcoupling of the members 20 and 22 is being done solely by the fluid F₂operably serving as a light shutter, the position of the interface Q maybe easily determined by the apparatus A. When the fluid F₁ is at thelevel or interface Q illustrated in FIG. 9, the edges of the radiatedand receivable light pattern or field is bounded by the dotted lines. Asthe level or interface Q moves or varies from that illustrated, the sizeof the communicated light field or quantity of light coupled by thefluid F₁ varies proportionally. The light quantity or intensity sensedfrom member 22 is thus a function of the location of the level orinterface Q of the fluid F₁.

It is understood that the case or housing (not illustrated in thisembodiment) enclosing the apparatus A prevents stray or spurious light,not from light conductor 20, entering receptor 22. The use of theembodiment of FIG. 9 as a fluid level sensor or detector apparatus Awill be readily apparent to those skilled in the art as noted above. Inaddition, this embodiment may be used to determine or sense fluidpressure by arranging the fluid system F₁ and F₂ to vary the interfacelevel in response to a pressure. This may be accomplished in any knownmanner or way. For example, any compression (increased pressure) ofcontained fluid F₂ will effect a change in the level or interface Q byliquid F₁ and which change varies the coupled light. In this embodimentthe light transmission geometric relationship of the member 20 and 22 isvaried solely by the change in level of the coupling fluid F₁ and theapparatus A is entirely passive in operation. The windows 20d and 22dcan be of any desired length to monitor movement of interface Q throughany preselected range of coupling fluid F₁. The roles of the members 20and 22 may also be reversed.

FIG. 10 discloses another embodiment of the present invention that issimilar to the embodiment of FIG. 9 in that the wave guides 20 and 22are fixed in physical relationship and the effective level of couplingfluid F₁ varies the apparent optical relationship. In this embodiment,the end cap 42 of the receptor member 22 is modified to extend outwardlyto provide a light reflective surface 34a with the end cladding 22c madeoptically transparent to capture the reflected light from mirroredsurface 34a. It is understood that the window 22d may have a replacementcladding 20c, 22c, of refractive index equal to or greater than that ofthe core 20a, 22a, for physical strength and light transmission. Thelight path emitted from the window 20d of member 20 is contained withinthe dotted line path as previously described. A portion of the lightemitted from the window 20d first strikes the reflective surface 42awhere they are reflected back toward the window 22d of the collectormember 22. Some of this reflected light is refracted or captured andtransmitted through the core 22a. Some of the light from window 20d isrefracted or directly captured in receptor member 22 and then reflectedby mirror surface 42a back to the sensor 28. In either coupled lightpath, the captured light in reflected by mirrored surfaces 34a, 42a inthe opposite direction to that of member 20.

As the size of the fluid coupled emitting window 20d of the member 20 iscontrolled by the interface level of the fluid F₁ the light madeavailable for detection is a function of the position of the level orinterface Q of fluids F₁ and F₂. One advantage of the arrangement of theembodiment of FIG. 10 is the compactness of the apparatus A insupporting both of the fiber optic members 20 and 22 at a common end.This is a highly desirable commercial feature or aspect and may beequally desirable in any form or embodiment of the apparatus A of thepresent invention.

FIG. 11 is yet another embodiment of the apparatus A of the presentinvention arranged in another commercially desirable form. In thisembodiment, the emitter member 20 is concentrically disposed within andadjacent the sleeve like collector member referenced in this embodimentas 122. Also in this embodiment, the relative positions of the member 20and 122 is fixed, but in a concentric relationship. The ring-shaped endmember 142 of the collector member 122 is reflective (mirrored) to lightin member 122, but opaque to prevent spray or random light entry throughend 122c (Due to the differing cylindrical shape, reference character122 is used to identify this receptor member with the suffix letterreference character used to designate like parts of member 22). Thefiber optic members 20 and 122 are compactly mounted in a cavity 123formed in an external transducer housing 137 and fixed in the spacedconcentric operating relationship by mutual cladding and spacingmaterial 138. The cylindrical member 137 also may serve as the outercladding for core 122. A cylindrical member 138 may be mutual claddingfor core 20 and cylindrical core 122. The housing 139 is formed of anyconvenient size, shape and configuration for appropriate mounting with asuitable cladding 137 adjacent and in communication with the specificcondition being sensed. Furthermore, the detailed manner of arranging,manufacturing, sealing, calibrating, assembly and installation of anytransducer apparatus A, as well as the preferred materials ofconstruction, are well known to those skilled in the art and need not bedetailed herein. The light collector window 122d in this embodiment isprovided by the cylindrical inner surface located adjacent the window20d of the emitter 20. As the level or interface Q of coupling fluid F₁rises, larger proportional light communicating areas of the windows 20dand 122d are optically coupled for communication more lighttherebetween. To enhance such light communication or capture, the endmember 130 of the emitter member 20 and end member 142 of collectormember 122 may be made internally reflective or mirrored in order thatlight will be coupled in the light ray path illustrated. Not only maythe interface Q be sensed, but by suitable arrangement of an expansiblechamber (not illustrated) containing the fluid F₁ other conditions, suchas pressure or temperature, may be sensed and converted into meaningfulproportional or indicator light signals.

FIGS. 15 and 16 illustrated an embodiment similar to that of FIG. 11,but employs the two separate, substantially identical fixed fiber optic20 and 22 used in FIG. 1. This embodiment employ a flexible tubularouter wall forming a protective housing 200 for the apparatus A. Thefiber optic members 20 and 22 are secured within the housing 200 in afixed parallel spaced apart relationship by a curable cement 201. Thecoupling fluid F-1 level in chamber 202 serves to optically communicatethe window 20d and 22d in the manner previously described. As theinterface Q moves along the window 20d and 22d a varying proportion oflight is coupled or communicated. A flexible diaphragm 204 or othersuitable chamber closure may be used to maintain the optical fluid F-1operably adjacent windows 20d and 22d.

The embodiment of FIG. 5 illustrates the apparatus of the presentinvention utilizing an external member M mounted with the apparatus A ina suitable manner to vary the light transmitted from the emitter member20 through the coupling fluid F to the receptor member 22.

The external member M may be of the type described in U.S. Pat. No.4,286,468 to Altmen relating to the hydrophone (acoustical pressure orsound wave transducer) which decreases or refracts the transmittedsignal. Such decrease or attenuation of the transmitted light may beutilized with the present invention when properly calibrated. Preferablythe external member M, is tubular shaped and supported in anyconventional known manner in essentially a concentric surroundingrelationship to the members 20 and 22. The inner surface 50 of themember M is formed optically reflective or mirrored for reflecting theincident light rays from the emitter 20 back to the collector 22.Preferably the member M is given an elliptical cross-section (FIGS. 6and 7) or an circular cross-section (FIG. 8) to focus the reflectedlight from the mirrored surface 50 on the collector window 22d in theknown manner. A light ray blocking shutter or shield (not illustrated)may be positioned to block any direct light path from the emitter 20 tothe collector 22 to enhance the operating effect of the member M. Whenthe fiber optic members 20 and 22 are optically centered as illustratedin FIGS. 6 and 7, the parabolic shaped halves of the member M form theradiating light ray path from the emitter 20 on the collector 22. As themember M moves relatively to the members 20 and 22 in the direction ofthe arrows in either FIGS. 6 or 7, the light rays formed by thereflection surface 50 are not longer properly focus or incident on thecollector 22 and the apparent collected light intensity decreases. Suchdecrease is proportional to the movement of the member M and can also bemeasured by the sensor 28.

In this embodiment, the fiber members 20 and 22 remain fixed (passive)in geometry while the member M moves to vary the sensed light. Themovement of the member M can be made proportionally responsive to thecondition being detected, such as pressure or temperature usingconventional techniques. It is not essential that member M move in theexact manner illustrated to produce a measurable change in the measuredlight intensity. A change in the cross-sectional shape of the member Mwill also create a misfocus or astigmatism type distortion of the focusto provide a proportional apparent decrease of light intensity in thecollector 22. Because the coupling fluid F may be selected from eithersubstantially incompressible to highly compressible silicone basedliquids, hydrophones capable of operation at great depths withoutpressure compensation are possible.

FIGS. 1 through 4 show embodiments in which the physical geometry of thefiber optic members may be varied or modified in order to proportionallyvary the amount of light transmitted to the collector. FIGS. 5 through 8show embodiments in which an external member proportionally varies thelight sensed by the collector. FIGS. 9 through 12 and 15 and 16 showembodiments with fixed fiber optic geometry and a coupling fluid thatvaries the amount of light transmitted to the collector.

FIGS. 1 through 5 show fiber optic members arranged for light passage inthe same direction while FIGS. 10 and 11 show opposite direction lightpaths.

In addition to providing a proportion output signal, the apparatus A mayalso be employed as part of an actuation signal or alarm system toindicated either a desired or undesired operating condition. Again, forexample and not limitation, the absence of coupling fluid from theapparatus A caused by the existence of a low level condition may be usedto trigger an alarm due to the decrease in apparent light collected.Either the presence or the absence of a certain strength of apparentlight signal in the collector member may be used as the trigger signal.Thus the apparatus may be used as an indicator of a condition (anon-proportional signal) as well as providing a proportional outputsignal. Such applications are virtually limitless in possibilities ofuse.

Each of the U.S. patents identified previously are included herein bythis specific reference to form a portion of this disclosure as if setforth in full.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, may be made without departing from the spirit of theinvention.

What is claimed is:
 1. A method of using a transducer to determine asensed condition, including the steps of:transmitting a light signalthrough a first fiber optic conductor; emitting at least a portion ofthe light signal from a side window means in a first fiber opticconductor to contact a light reflective surface means; couplingoptically the first and second fiber optic conductors with a preselectedfluid medium; capturing at least a portion of the emitted light signalfrom the first fiber optic contacting said light reflective surface witha second fiber optic conductor; transmitting the light signal capturedby the second fiber optic conductor through the second fiber opticconductor; sensing a value for the light signal conducted through thesecond fiber optic conductor; and determining the condition sensed bycomparing the sensed value for the light signal conducted through thesecond fiber optic conductor with a reference value; changing therelative position of an external the light reflective surface means inresponse to the sensed condition to proportionally control the capturedportion of the emitted light signal.
 2. A method of using a transducerto determine a sensed condition, including the steps of:transmitting alight signal through a first light conductor; emitting at least aportion of the light signal from the first light conductor to contact alight-reflective surface means; capturing at least a portion of theemitted light signal from the first light conductor contacting theexternal surface of the optical member with a side window mans of asecond light conductor; transmitting the light signal captured by thesecond light conductor through the second light conductor; sensing avalue for the light signal conducted through the fiber optic conductor;and determining the condition sensed by comparing the sensed value forthe light signal conducted through the second light conductor with areference value; coupling optically the first and second lightconductors with a preselected fluid medium; and changing the relativeposition of the light reflective surface means in response to the sensedcondition to proportionally control the captured portion of the emittedlight signal.
 3. A transducer apparatus for producing a useful outputlight signal in response to a sensed condition, including:a housingadapted for placement in operable communication with the condition to besensed and having first and second fiber optic members operably mountedtherewith; means for optically connecting said first fiber optic memberwith a source of light; means for optically connecting said second fiberoptic member with an appropriate light sensor; said first fiber opticmember having a side windows means for emitting a predetermined lightpattern; said second fiber optic member having means for capturing atleast a portion of the light emitted from the first fiber optic memberfor transmitting to the light sensor; and means for varying the lightcollected by the second fiber optic member in response to the sensedconditions being transduced to provide a useful output signal; saidhousing forming a chamber for receiving a coupling fluid having apreselected index of refraction for directing the emitted light in adesired path for capture by said second fiber optic member; said meansfor varying provides a proportional change in the light collected bysaid second fiber optic member in response to a change in the sensedcondition to provide a useful range of output signals; and said meansfor varying including light directional control means mounted with saidhousing and operably disposed in the emitted light path between saidfirst and second fiber optic members for moving in response to thesensed condition to vary the emitted light collected by said secondfiber optic member.
 4. A transducer apparatus for producing a usefuloutput light signal in response to a sensed condition, including:ahousing adapted for placement in operable communication with thecondition to be sensed and having first and second light conductormembers operably mounted therewith; means for optically connecting saidfirst light conductor member with a source of light; means for opticallyconnecting said second light conductor member with an appropriate lightsensor; said first light conductor member having means for emitting apredetermined light pattern; said second light conductor member having aside window means for capturing at least a portion of the light emittedfrom the first conductor member for transmitting to the light sensor;and means for varying the light collected by the second light conductormember in response to the sensed conditions being transduced to providea useful output signal; said housing forming a chamber for receiving acoupling fluid having a preselected index of refraction for directingthe emitted light in a desired path for capture by said second lightconductor member; said means for varying provides a proportional changein the light collected by said second light conductor member in responseto a change in the sensed condition to provide a useful range of outputsignals; and said means for varying including light directional controlmeans mounted with said housing and operably disposed in the emittedlight path between said first and second fiber optic members for movingin response to the sensed condition to vary the emitted light collectedby said second light conductor member.
 5. A light coupler, including:afirst dielectric waveguide for emitting a light signal, said firstdielectric having a means for emitting the light signal in apredetermined path; a second dielectric waveguide having side windowmeans for receiving the light signal emitted by said first dielectricwaveguide, said second dielectric waveguide having a side window forreceiving the light signal; a coupling fluid of preselected refractiveindex for optically coupling said first dielectric waveguide with saidsecond dielectric waveguide; and means, disposed in the path of thelight signal emitted from said first dielectric waveguide, forcontrolling the light path direction between said first and seconddielectric waveguides in response to a sensed condition by changing theposition of said means for controlling the light path direction betweensaid first and second dielectric waveguides to control the emitted lightcollected by said second waveguide.
 6. The light coupler of claim 5,wherein:said first and second dielectric waveguides are operably fixedrelative to each other.
 7. The light coupler of claim 5, wherein:saidfirst and said second dielectric waveguides are operably movablerelative to each other.
 8. A light coupler, including:a first dielectricwaveguide for emitting a light signal, said first dielectric having aside window means for emitting the light signal in a predetermined path;a second dielectric waveguide having means for receiving the lightsignal emitted by said first dielectric waveguide; a coupling fluid ofpreselected refractive index for optically coupling said firstdielectric waveguide with said second dielectric waveguide; and means,disposed in the path of the light signal emitted from said firstdielectric waveguide, for controlling the light path direction betweensaid first and second dielectric waveguides in response to a sensedcondition by changing the position of said means for controlling thelight path direction between said first and second dielectric waveguideto control the emitted light collected by said second waveguide.
 9. Thelight coupler of claim 8, wherein:said first and said second dielectricwaveguides are operably fixed relative to each other.
 10. The lightcoupler of claim 8, wherein:said first and said second dielectricwaveguides are operably movable relative to each other.